1. Field of Invention
The present invention relates to a gear shifting method of a hybrid vehicle that combines an engine and a motor to generate a rotation torque and to transfer the rotation torque to an output shaft through a transmission.
2. Description of Related Art
Generally, an automatic transmission uses a hydraulic pressure to shift gear in a multi steps so as to output appropriate torque from a rotation torque of an engine/motor according to a driving condition.
One type of hybrid vehicles uses two motor/generators (MG) and one engine that are connected through a planetary gear and controls the motor/generator to achieve a continuous variable shifting.
Meanwhile, clutches and brakes are released so as to prevent a torque from being transferred to an output shaft of the transmission in a parking (P) or neutral (N) condition.
When it is transferred from a parking or neutral condition of a transmission to a drive (D) or reverse (R), slip is formed in the clutch and the brake by a rotation speed difference such that vibration/noise is formed by the frictional force and the durability of the transmission is decreased.
FIG. 4 is a table showing a gear shifting method of a conventional hybrid vehicle.
Referring to FIG. 4, an engine is controlled in an idle speed in a neutral (N) or parking (P). In other words, output torque of the engine is controlled according to an idle target speed. Further, a speed of the first motor/generator is controlled so as to prepare an EVT1 mode or an EVT2 mode for a next drive (D) or reverse (R) and an output torque of the second motor/generator is controlled for charging and discharging according to a target torque.
Meanwhile, since an engine is controlled to have an idle target speed in a neutral or parking state and an engine is controlled to output a predetermined torque in a driver or reverse state, there is a problem that a shift shock is generated and fuel consumption is increased.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.